In vitro anticryptosporidial activity of ranalexin alone and in combination with other peptides and with hydrophobic antibiotics

The in vitro activity of ranalexin alone and in combination with other cationic peptides, macrolides, rifampin, and rifabutin was investigated against a clinical isolate of Cryptosporidium parvum. Susceptibility tests were performed by inoculation of the isolate onto cell monolayers and determining the parasite count after 48 h of incubation at 37 degrees C. Antibiotic-free cultures were used as controls in the study. Ranalexin showed low anticryptosporidial activity: it suppressed the growth of parasites by greater than or equal to 40% at 50 mu M. Ranalexin showed enhanced activity when it was combined with noninhibitory concentrations of other compounds: a 74.4-94.1% reduction in the number of parasites was observed when ranalexin 50 mu M was combined with magainin II 50 mu M, indolicidin 50 mu M, clarithromycin 8 mg/l, azithromycin 8 mg/l, rifampin 8 mg/l, and rifabutin 8 mg/l, The results suggest that ranalexin may be effective in inhibiting Cryptosporidium parvum growth in vitro upon combination with other peptides and hydrophobic antibiotics.